Laser oscillator

ABSTRACT

A laser oscillator that, in accordance with a laser output instruction value or a current instruction value that is input, excites a laser medium and obtains a desired laser output comprises: reference waveform generation unit for employing the laser output instruction value or the current instruction value to generate a laser output waveform and a current waveform, which are references; a first comparison unit for obtaining, as a current monitor value, a current value used to excite the laser medium, and for comparing the current value with the current wave form generated by the reference wave form generation unit; and a second comparison unit for fetching, as a laser output monitor value, the value of a laser that is output by exciting the laser medium, and for comparing the value for the laser with the laser output waveform generated by the reference waveform generation unit, wherein an abnormality is detected.

TECHNICAL FIELD

The present invention relates to abnormality determination unit fordetecting a failure of a laser oscillator, according to which it can beprecisely determined whether an abnormality of a laser beamamplification portion or an abnormality of a portion related to a powersource has occurred, and the location of the failure can be easilyidentified.

BACKGROUND ART

FIG. 11 is a schematic diagram showing the configuration of a laseroscillator. In FIG. 11, reference numeral 1 denotes a laser diode thatemits light when a direct current is received from a power supply device10; 2, denotes a laser medium; 3, a total reflection mirror; 4, apartial reflection mirror; 5, an expansion lens for expanding a laserbeam; 6, a parallel shifting lens for changing a laser beam intoparallel beams; 7, an optical fiber entrance lens; 8, an optical fiber;9, a machine head; and 10, a power supply device.

By supplying a direct current to the laser diode 1, light is emitted,the laser medium 2 is excited, and resonance is generated between thetotal reflection mirror 3 and the partial reflection mirror 4. As aresult, a laser beam is obtained.

The thus obtained laser beam is expanded by the expansion lens 5 and ischanged into parallel beams by the parallel shifting lens 6, and theobtained beams are concentrated at the end face of the optical fiber 8by the optical fiber entrance lens 7. Then, the concentrated laser beampasses through to the inside of the optical fiber 8 and is guided to apredetermined location through the machine head 9.

The laser output can be adjusted by varying the current supplied to thelaser diode 1. Generally, a predetermined laser output or a currentinstruction is externally transmitted to the power supply device 10 thatsupplies current to the laser diode 1, and the power supply device 10then controls the current that is to be supplied to the laser diode 1.

FIG. 12 is a diagram showing a specific internal example for the powersupply device 10. First, the basic operation of the power supply device10 will be described.

In the power supply device 10, input power is transformed into a directcurrent by a rectifier 16, and the direct current charges a capacitor17.

Then, a transistor 13 is turned on, and a current begins to flow to thelaser diode 1 through a reactor 14.

The amount of current flowing to the laser diode 1 is increased whilethe transistor 13 is on, and when the amount of the current exceeds adesired current value, the transistor 13 is turned off to decrease thecurrent.

When the amount of the current falls below the desired current value,the transistor 13 is turned on to increase the current.

By repeating the turning on and off of the transistor 13, the amount ofcurrent is adjusted to obtain the desired current value.

An example on and off control process is, as is shown in FIG. 13, ahysteresis comparator control process wherein the ON and OFF states arecontrolled within a range extending from the upper to the lower limitcurrent values that are provided, or a PWM control process wherein theON time is controlled during a specific period of time.

The control process will now be described in detail while referring toFIG. 12.

A current controller 18 fetches a desired current value (currentinstruction value), and the value of a current that is obtained througha current sensor 12, that is appropriately controlled by a gainadjustment unit 20, and that is currently flowing.

In the hysteresis comparator control process, these two types of dataare fetched by a comparator 21, and the comparator 21 compares the datawith a current value for turning on the transistor 13 and a currentvalue for turning off the transistor 13, both of which are set inadvance, and determines whether the transistor 13 should be turned on oroff.

Though not shown in FIG. 12, in the PWM control process a differencebetween the two types of data is calculated by a microcomputer, and theON time is controlled within a specific period of time.

The thus obtained ON or OFF instruction of the transistor 13 istransmitted to a circuit for driving the transistor 13 (a circuit that,based on a logic signal received from a control system, supplies thecurrent or the voltage actually required to turn the transistor 13 on oroff). As a result, the transistor 13 is turned on or off.

Through these operations, the power controller 18 fetches a desiredcurrent value, and adjusts the current to match the desired currentvalue.

The control process for obtaining a desired laser output value will nowbe described.

The power controller 18 fetches a desired laser output instruction valueand a laser output monitor value (current laser output) that istransmitted through a laser output monitor sensor 11.

The power controller 18 calculates a difference between the obtaineddata, and adjusts a presently available current instruction value.

Based on the adjusted current instruction value, the transistor 13 isturned on or off in the same manner as when an externally supplied,desired current value is received.

A switch 19 is a selection switch used to validate a current instructionor a laser output instruction.

A solid-state laser oscillator, which is controlled as described above,is used for welding or cutting metal.

When a desired laser output can not be maintained, a welding failure ora cutting failure occurs. Thus, means is required for providing anexternal alarm warning that an abnormality has occurred when the desiredlaser output can not be maintained.

As example means for providing an external alarm when an abnormality hasoccurred and the desired laser output can not be obtained, for a minimumrequired laser output of 200 W, a circuit 25 is additionally providedthat is turned on when the laser output monitor value reaches 200 W, andthat transmits an ON signal to an oscillator controller 26. Further,awaiting period for the ON signal is defined, and when the signal is notrendered on within the allocated period of time, an abnormalitynotification is provided.

Further, in an example wherein an upper laser output limit is defined toprevent too much welding power, a maximum 300 W is set as the upperlimit value, and a circuit 24 is additionally provided that is turned onwhen the laser output exceeds the upper limit. Using this ON signal, anabnormality notification can be provided.

In addition, a maximum available current is defined for the laser diode1, and when a current equal to or greater than the defined value issupplied, an abnormality occurrence notification must be givenexternally.

When, for example, the laser diode 1 will be damaged when a current of50 A or greater is supplied, a circuit 23 is additionally provided thatis turned on when the current monitor value obtained by the currentsensor 11 is greater than 50 A. This ON signal is transmitted to theoscillator controller 26 as an abnormality notification.

Based on this ON signal, the oscillator controller 26 performs anappropriate process (e.g., a power cutoff) and protects the laser diode1.

An example arrangement for protecting the laser diode 1 has beenexplained. However, when the value of a current that can flow to anotherdevice, such as the transistor 13 or the reactor 14, is lower than theavailable value of a current flowing to the laser diode 1, the definedcurrent value must be changed in accordance with the other device.

As is described above, since the solid-state laser oscillator has meansfor providing an external notification for a laser output abnormality, awelding or cutting failure can be prevented.

Furthermore, when a current flows that is equal to or greater than adefined value, the means for providing an external notification of anabnormality protects the individual devices.

When both an abnormality resulting from the laser output exceeding anupper limit and an abnormality resulting from a current value exceedinga defined value occur at the same time, the above described conventionalsolid-state laser oscillator can determine whether too much current hasbeen supplied to the laser diode 1, and can also determine whether thelaser output exceeded the upper limit because of the power supplyabnormality.

A power supply abnormality is an abnormality other than one for thelight amplification portion (damage to a PR mirror or a TR mirror)excluding the laser diode 1 in FIG. 1. An example abnormality is thefailure of a device used to supply power.

However, merely by providing notification that an abnormality hasresulted from the laser output exceeding an upper limit (an abnormalityresulting from a current value exceeding a defined value has notoccurred), whether there is a power supply abnormality can not bedetermined.

While referring to FIG. 12, an explanation will now be given for anexample laser oscillator wherein the lower output limit value is 200 W,the upper limit value is 300 W, and the maximum defined current value is50 A; wherein a laser output of 250 W is obtained when a current of 20 Ais supplied, and a laser output of 350 W is obtained when a current of40 A is supplied; and wherein a desired current instruction value is 20A.

When 0.5 times an actual current value is returned to the comparator 21,as the current monitor value obtained by the current sensor 11, becausean abnormality has occurred at the gain adjustment unit 20, (1/0.5)times a current, i.e., 40 A, is actually supplied to the laser diode 1,while a current of 20 A was originally transmitted to the laser diode 1.Therefore, a 350 W laser is output.

Thus, conventionally, it can be determined that an abnormality hasoccurred wherein the laser output exceeds the upper limit. At this time,since the current actually flowing across the laser diode 1 is 40 A,which is equal to or lower than the maximum defined current value, anabnormality that occurs when the current value exceeds the defined valueis not detected.

Generally, an abnormality in a light amplification portion is assumed tobe an abnormality that occurs when the laser output exceeds the upperlimit. In this case, however, it should be determined that anabnormality has occurred, not at the light amplification portion but atthe gain adjustment unit 20 of the current controller 18, i.e., that apower supply abnormality has occurred. This abnormality can not beprecisely detected.

In addition, when wiring extended to the laser diode 1 is cut off, acurrent does not flow to the laser diode 1, and accordingly, no laser isoutput.

Therefore, the laser output is reduced, to below the lower limit, and alaser output abnormality occurs.

At this time, since a current does not flow across the laser diode 1, anabnormality resulting from the current value exceeding the defined valuedoes not occur.

Also in this case, it should be determined that the abnormality has notoccurred at the light amplification portion, but that the abnormality,i.e., a power cutoff, has occurred at the power supply portion. However,the power supply abnormality can not be designated merely by detectingthe laser output abnormality.

This is because, since the detection of the power supply abnormality isperformed in order to protect the power supply body (to protect devicessuch as the laser diode 1 and the transistor 13), a power supplyabnormality that would cause a welding failure or a cutting failure isdetected as the laser output abnormality.

That is, the conventional laser oscillator can detect the laser outputabnormality to prevent the occurrence of a welding failure or cuttingfailure. However, whether the abnormality has occurred at the lightamplification portion or the power supply portion can not be determined,for it is difficult to identify the location of the abnormality, and tocope with the abnormality, an extended period of time is required.

DISCLOSURE OF THE INVENTION

To resolve these problems, it is one objective to provide an apparatusthat can prevent a welding failure or a cutting failure, and that caneasily identify the location of the failure.

To achieve this objective, according to a first aspect of the invention,a laser oscillator that, in accordance with a laser output instructionor a current instruction value that is input, excites a laser medium andobtains a desired laser output comprises:

reference waveform generation unit for employing the laser outputinstruction value or the current instruction value to generate a laseroutput waveform and a current waveform, which are references;

a first comparison unit for obtaining, as a current monitor value, acurrent value used to excite the laser medium, and for comparing thecurrent value with the current waveform generated by the referencewaveform generation unit; and

a second comparison unit for fetching, as a laser output monitor value,the value of a laser that is output by exciting the laser medium, andfor comparing the value for the laser with the laser output waveformgenerated by the reference waveform generation unit,

wherein an abnormality is detected.

The laser oscillator further comprises:

a third comparison unit for fetching an ON/OFF signal for a main circuitdevice for controlling a current that flows across a laser diode thatexcites the laser medium or a monitor signal for the main circuitdevice, and for comparing the ON/OFF signal with an ON/OFF signal forthe main circuit device that is generated by the reference waveformgeneration unit based on the laser output instruction or the currentinstruction value.

Furthermore, for the comparison performed by the comparison unit, apredetermined permissible range is set for a reference waveform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the configuration of a laseroscillator according to a first embodiment of the invention;

FIG. 2 is a flowchart showing the abnormality determination processing;

FIG. 3 is a diagram for explaining an equivalent circuit in a laserdiode;

FIG. 4 is a diagram showing a current waveform;

FIG. 5 is a graph showing an approximation of the current waveform;

FIG. 6 is a graph showing an abnormality determination sequence;

FIG. 7 is a graph showing a permissible range set for a secondembodiment;

FIG. 8 is a schematic diagram showing the configuration of a laseroscillator according to a third embodiment;

FIG. 9 is a diagram showing the determination performed for the ON/OFFwaveform of a transistor;

FIG. 10 is a diagram showing the generation of the ON/OFF waveform ofthe transistor;

FIG. 11 is a schematic diagram showing the configuration of aconventional laser oscillator;

FIG. 12 is a diagram showing a specific internal example for a powersupply device 10; and

FIG. 13 is a diagram for explaining hysteresis comparator control andPWM control.

BEST MODES FOR CARRYING OUT THE INVENTION

First Embodiment

FIG. 1 is a diagram showing the configuration of a laser oscillatoraccording to a first embodiment of the present invention.

First, the basic operation of a power supply device 10 will bedescribed.

In the power supply device 10, the power that is input is transformedinto a direct current by a rectifier 16, and the direct current is usedto charge to a capacitor 17.

A transistor 13 is turned on, and a current begins to flow through areactor 14 to a laser diode 1.

Thereafter, the current flowing across the laser diode 1 is increasedduring a period wherein the transistor 13 is on, and when the strengthof the current exceeds a desired current value, the transistor 13 isturned off to decrease the current.

When the current strength falls below the desired current value, thetransistor 13 is turned on to increase the current.

By repeating the turning on and off of the transistor 13, the currentstrength is adjusted to the desired current value.

The ON/OFF timing control, as is shown in FIG. 13, explained for theconventional example, can be a hysteresis comparator control processwherein the transistor 13 is turned on or off within a range extendingfrom the upper limit to the lower limit provided for the current value,or the PWM control process wherein the ON time is controlled within aspecific, limited time period.

The control process will now be described in detail while referring toFIG. 1.

A power controller 18 fetches a desired current value (currentinstruction value) and the value of the current that is currentlyflowing, and is appropriately controlled through a current sensor 12 bya gain adjustment unit 20.

During the hysteresis comparator control process, the two types of dataare fetched to a comparator 20. The comparator 20, then compares thedata with current values, which have been set in advance, for turning onthe transistor 13 and for turning off the transistor 13, and determineswhether the transistor 13 should be turned on or off.

Whereas although not shown, in the PWM control process a differencebetween the two types of data thus fetched is calculated by amicrocomputer, and the ON time is increased or reduced during aspecified time period.

The operation of an abnormality determination unit 22, which is thefeature of the embodiment, will now be described.

A conventional abnormality determination unit determines that anabnormality has occurred by comparing a current control value, an upperlaser output limit value and a lower laser output limit value, all ofwhich have been set in advance, with a current monitor value and a laseroutput monitor value that have been obtained. In this embodiment, theabnormality determination unit obtains a current instruction value and alaser output instruction value, and compares them with a current monitorvalue and a laser output monitor value that have been obtained.

FIG. 2 is a flowchart showing the abnormality determination processingperformed by the abnormality determination unit. The schematicabnormality determination operation will now be explained whilereferring to the flowchart in FIG. 2.

At step S1, either the current instruction value or the laser outputinstruction value are entered. It should be noted that, in this case,either only the current instruction value or the laser outputinstruction value need be entered. At step S2, either a current waveformor a laser output waveform is generated as a reference consonant withthe instruction value (hereinafter the current or laser output waveform,which is a reference consonant with the instruction value, is calledeither a reference current waveform or a reference laser outputwaveform).

At step S3, the reference waveforms are employed to set a permittedrange even when the actual current, which is a current monitor valuedetected by a current sensor 12, and a laser output, which is the laseroutput monitor value input through a laser output monitor sensor 11,differ from the instruction values.

At step S4, a comparator 28, which is a first comparison unit, comparesthe current monitor value with the permissible range, and when thecurrent monitor value exceeds the permissible range, the existence of anabnormality is determined at step S5, and an error signal is output tothe oscillator controller 26.

At step S6, a comparator 29, which is a second comparison unit, comparesthe laser output monitor value with the permissible range, and when thelaser output monitor value exceeds the permissible range, the existenceof an abnormality is determined at step S7 and an error signal is outputto the oscillator controller 26.

The operation performed at steps S1 through S7 is repeated to monitorthe solid-state laser oscillator.

An explanation will now be given for an example wherein the currentinstruction value and the laser output instruction value are employed togenerate the reference current waveform and the reference laser outputwaveform.

First, an explanation will be given for the generation of the referencecurrent wave form using the current instruction.

In FIG. 1, when the transistor 13 is on, the reference current waveformis a rising waveform determined by the characteristics of the reactor 14and the laser diode 1, which serves as a load.

Since, as is shown in FIG. 3, the characteristic of the laser diode 1can be approximated using a resistor R and a direct-current voltagesource V, the current value is substantially increased linearly, as isshown in FIG. 4.

When the inductance value of the reactor 14 is denoted by L1 and theapproximate resistance of the laser diode 1 is denoted by R1, theinclination of the current, depicted by a rising waveform, is determinedto be a constant α, in accordance with the value (R1/L1). Since thisconstant α is a persistent value when the characteristics of the reactor14 and the laser diode 1 are not changed, by employing the followingequation, the rising waveform of the current can be represented using α,so long as the characteristics are unchanged:currentI=inclinationα×time t.

Since the constant α is a persistent value, regardless of the currentinstruction value, the time required for the current value to attain adesired value differs, depending on the current instruction value.

When the current instruction value is denoted by I1, the period requiredfor the current value to reach I1 is represented by (I1/α).

Therefore, the current can be represented by the following functions:I=×twhen 0≦t≦(I 1/α)  Equation 1I=I 1 when (I 1/α)≦t  Equation 2

Since the current is represented by the functions, this current can beused as the reference current waveform.

It should be noted that the characteristic of the laser diode 1 can beapproximately represented by employing a comparatively simple functionthat uses the resistance and the power voltage. However, somecharacteristics of the laser diode 1 can not be represented simply byusing the resistance and the power voltage. For this, the currentwaveform must be actually measured and the function of an approximatecurve must be obtained and used as the reference current waveform.

Another method, as is shown in FIG. 5, is a method for performing astepped approximation of an actual current waveform. According to thestepped approximation method, the current value between time t1 and timet2 is adjusted so it approximates that of Ia, and the current valuebetween the time t2 and time t3 is adjusted so it approximates that ofIb.

An extreme approximation example is shown in FIG. 5 b, wherein thecurrent value is defined as 0 from time t0 to time tx, whereat a desiredcurrent value I1 is obtained, and the current value following time tx isdefined as the desired current value.

In this manner, the reference current waveform can be generated inaccordance with the current instruction.

An explanation will now be given for an example wherein the referencelaser waveform that is output is generated in accordance with thecurrent instruction.

In this case, the function of the relationship between the current valueand the laser output can be obtained by substituting this function intothe above function for the reference current waveform.

Since the laser output is increased in proportion to the increase in thecurrent when a threshold current (the minimum current amount requiredfor laser oscillation) is exceeded, the relationship between the currentI and a laser output P can be represented asP=β×(1−γ)  Equation 3wherein β denotes a proportional constant and γ denotes a thresholdcurrent.

When the reference current waveform is represented by the functions ofequations 1 and 2, the laser output can be represented by the followingfunctions:P=β×(α×t−γ) when 0≦t≦(I 1/α)  Equation 4P=β×(I 1−γ) when (I 1/α)≦t  Equation 5

Since the laser output is represented by these functions, the values canbe used for the reference laser waveform that is output.

When the relationship between the current value and the laser output cannot simply be represented as in equation 3, the laser output waveformmust actually be measured, and the function for the approximate curvemust be obtained for use as the reference laser output waveform.

While the stepped approximation is performed to obtain the referencecurrent waveform in accordance with the current instruction value, thereference laser output wave form can also be obtained, in the samemanner, by the stepped approximation.

An explanation will now be given for an example wherein the referencecurrent waveform is generated in accordance with the laser outputinstruction.

The current amount is continuously increased until the laser outputmonitor value reaches the laser output instruction value. When the laseroutput instruction value is reached, the current is set to a constantvalue.

When the current value, which is the laser output instruction value P1,is denoted by Ip1, the waveform for this current is obtained byreplacing the current instruction value I1 with Ip1 to acquire thereference current waveform.

For example, when the current instruction value, the actual currentvalue and the laser output value are represented by equations 1, 2 and3, based on equation 3, the current value I1p, which is the laser outputinstruction value P1, is represented as follows:Ip 1=(P 1/β)+γ  Equation 6

Therefore, from equations 1 and 2,I=α×twhen 0≦t≦(((P 1/β)+γ)/α)  Equation 7I=(P 1/β)+γ when (((P 1/β) +γ)/α)≧t  Equation 8

Since the current is represented by these functions, an obtained valuecan be used as the reference current waveform.

While the reference current waveform and the reference laser outputwaveform have been obtained in accordance with the current instructionvalue, the current waveform may be actually measured and the functionfor the approximate curve may be obtained for use as the referencecurrent waveform, or the stepped approximation may be performed and theobtained waveform may be used as the reference current waveform.

Next, an explanation will be given for an example for generating areference laser output waveform in accordance with a laser outputinstruction.

As is described in the example for generating, in accordance with acurrent instruction, the reference laser output waveform, the referencelaser waveform that is output, can be obtained by substituting thefunction representing the relationship, between the current value andthe laser output value, into the function representing the referencecurrent waveform.

For example, when the reference current waveform is represented byequations 7 and 8, based on equation 3,P=β×(α×t−γ) when 0≦t≦(((P 1/β)+γ/α)  Equation 9P=P 1 when (((P 1/β)+γ)/α)≦t  Equation 10

Since the laser output can be represented by using the function, it canbe used as a reference laser output waveform.

Naturally, the laser output waveform may actually be measured and thefunction for an approximate curve may be obtained for use as a referencelaser output waveform, or the stepped approximation process may beperformed and the results may be used as the reference laser outputwaveform.

In the above examples, a constant value has been set upon the rise ofthe current and the output of the laser. For a case wherein it falls,the reference waveform can be generated in the same manner. When acurrent instruction or a laser output instruction is not issued, i.e.,when a current value of 0 A or a laser output of 0 W is instructed,naturally, the reference waveform for the current value of 0 A or thelaser output of 0 W can be generated.

A permissible range must be set to cope with a case wherein the actual,current monitor value and the laser output monitor value differ from thereference current waveform and the thus obtained reference laser outputwaveform.

This range should be set because, since a variance is present in thecharacteristics of the laser diode 1, which serves as a load, and thereactor 14, the actual waveforms may differ from the referencewaveforms.

To determine the permissible range, the following points must be takeninto account:

1. a variance in the inclination of a current due to a variance in thecharacteristics of the reactor and the laser diode,

2. parallel shifting of a current value due to the offset shifting of acurrent sensor (although a current value 0 A is actually output, thesignal for a sensor is output as if a 1 A current was flowing)

3. variances in the maximum current value and the minimum current valueproduced by turning on and off the transistor (a difference between theON current value and the OFF current value of the transistor in FIG. 13)The permissible range can be determined through a discussion of theabove entries. While a specific value for this range will not bedescribed in detail because, depending on the power supply device, itwill differ, a method for setting the permissible range will beexplained.

Since the same method is employed both for the reference currentwaveform and the reference laser output waveform, an explanation will begiven only for the reference current waveform.

Whether an abnormality has occurred is determined after the permissiblerange has been set. For this abnormality determination, a distance ismeasured whereat a monitor value is shifted from the reference waveformat a specific time.

Or a difference between the time whereat a specific reference current isreached and the reference value is measured to determine whether anabnormality has occurred. The two methods described above can beemployed and a permissible range set in different manners.

Therefore, to measure a difference between the monitor value at aspecific time and the reference value, maximum and minimum monitorvalues permitted at the specific time must be set, as is shown in FIG. 6a.

As is shown in FIG. 6 b, to measure a difference between the timewhereat a specific reference current is reached and the reference timevalue, the width must be set for the time whereat the reference currentis reached, as shown in FIG. 6 b.

In this case, after a constant current has been reached, thedetermination process must be changed to a process for determining adifference between a monitor value at a specific time and the referencevalue.

The permissible ranges need not always be constant values, and may bevaried in correlation with the current instruction value and the laseroutput instruction value, or they may be changed as time elapses.

After the permissible ranges have been set, these ranges are comparedwith the current monitor value and the laser output monitor value.

During this comparison process, as is described above, differencebetween the monitor value at a specific time and the reference value, ora difference between the time whereat a specific reference current isreached and the reference time value is measured, and when thedifference falls outside the reference range, it is determined that anabnormality has occurred. An error signal is then output to theoscillator controller 26.

The comparison timing may be monitored constantly, or may, under thecontrol of a microcomputer, be monitored at regular intervals todetermine whether the difference in time falls outside the referencerange.

Since in many cases cutting or welding is performed when a constantlaser output is obtained, the comparison process may not be performedbefore the current or the laser output becomes constant, and may bestarted after it becomes constant.

In this embodiment, through the above described operation, whether themonitor value falls outside the reference waveform is detected, and awelding failure or a cutting failure is prevented. Further, when a laseroutput abnormality has occurred, it can be precisely determined whetherthe abnormality is related to the light amplification portion or to thepower supply portion, and the location of the failure can be easilyidentified.

An explanation will now be given for an example performed under the sameconditions as those used for the explanation given for the conventionalexample, i.e., wherein the lower limit and the upper limit of the outputcontrol value are respectively 200 W and 300 W and the maximum definedcurrent value is 50 A, wherein a laser output of 250 W is obtained bysupplying a current of 20 A and a laser output of 350 W is obtained bysupplying a current of 40 A, and wherein a desired current instructionvalue is 20 A.

When the occurrence of an abnormality at the gain adjustment amplifier20 is detected in accordance with the current monitor value output bythe current sensor 11, and when 0.5 times the actual current value isoriginally returned to the comparator 21, a current of 20 A is supposedto flow to the laser diode 1. However, actually, (1/0.5) times thecurrent, i.e., 40 A, is supplied to the laser diode 1, and a laser isoutput at 300 W. Thus, it can be determined that there is a laser outputabnormality.

In the conventional example a power supply abnormality does not occur.In this invention, however, when it is set up so that an abnormality isdetected when there is a difference of at least 3 A, for example, fromthe reference waveform, since an actual current of 40 A differs from thereference waveform of 20 A by more than 3 A, it can be determined thatthere is a power supply abnormality.

That is, although no abnormality is detected for the light amplificationportion, an abnormality has occurred for the gain adjustment amplifier20 of the current controller 18, and it can be correctly determined thatthe abnormality is related to the power supply portion.

On the other hand, when the power on the line to the laser diode 1 iscut off, the laser output value is lower than the lower limit of thecontrol value, and a laser output abnormality occurs. And in addition,since there is no current flow, the waveform differs from the referencewaveform, thereby indicating that a power supply abnormality has alsooccurred.

Therefore, it can be determined that the laser output abnormalityoccurred due to the power supply abnormality.

Assume that a power abnormality has not occurred, even though there is alaser output abnormality. According to the conventional example, sincethe waveform of the current that is actually flowing is not comparedwith the reference waveform, whether or not the current is beingcorrectly supplied to the laser diode 1 (is flowing in accordance withthe reference waveform) can not be determined, and accordingly, adecision can not be made as to whether no abnormality has occurred inthe power supply portion.

According to the invention, however, since the waveform of the currentthat is actually flowing is compared with the reference waveform, it isapparent that the current is being correctly supplied to the laser diode1 (is flowing in accordance with the reference waveform), and it can bedetermined that an abnormality has occurred at the light amplificationportion, and that no abnormality has occurred at the power supplyportion.

Furthermore, since the laser output is constantly monitored to detectany abnormality, a cutting failure or a welding failure does not occur.

As is described above, as the feature of the invention, the currentmonitor value, which is detected through the current sensor 12, and thelaser output monitor value, which is received through the laser outputmonitor sensor 11, are compared with the reference current waveform andthe reference laser output waveform, which are obtained in accordancewith a current instruction value and a laser output instruction valuethat are externally input and received. When the monitor values differ,an individual operating the laser is notified an abnormality hasoccurred. Therefore, a cutting failure and a welding failure areprevented, and when a laser output abnormality has occurred, it can beprecisely determined whether the abnormality has occurred at the lightamplification portion or at the power supply portion. As a result, thelocation of the failure can be easily identified.

Second Embodiment

According to a second embodiment, the method used for setting areference waveform differs from that for the first embodiment, as isshown in FIG. 7.

In the first embodiment, different reference waveforms are generatedbased on the current instruction value and the laser output instructionvalue, while in the second embodiment, reference waveforms are generatedbased on the representative values of the current instruction value andthe laser output instruction value.

As a representative value, either the maximum value for the currentinstruction or the laser output instruction, or a center value may beemployed.

By using the representative value for the reference waveform, apermissible range can be set while taking into account not onlyvariances produced by the components of a power source, but also achange in the current monitor value or the laser output value when thecurrent instruction or the laser output instruction differs.

Further, as another method for generating a reference waveform, theminimum and maximum current instruction values may be employed to setthe reference waveform and to set a predetermined permissible range. Asa result, the same effects can be obtained as are obtained in the firstembodiment.

Third Embodiment

According to a third embodiment, in addition to the configuration of thefirst embodiment, an ON/OFF signal for the transistor 13 is transmittedto a comparator 30 that corresponds to the third comparison unit of theabnormality determination unit 22 (FIG. 8).

The ON/OFF signal for the transistor 13 is used when measuring a voltagechange in the gate drive device of the transistor 13.

As another method, a potential difference between the collector voltagefor the transistor and the negative electrode potential of the capacitoris measured (portion a in FIG. 8). When the difference is the same asthe positive potential of the capacitor, it can be assumed that thetransistor is in the ON state, and when the difference is the same asthe negative potential of the capacitor, it can be assumed that thetransistor is in the OFF state. Thus, the voltage change may be employedas an ON/OFF signal for the transistor.

In this embodiment, the ON/OFF signal for the transistor can bemonitored in the described manner.

Also, for an ON/OFF signal for the transistor, a reference transistorON/OFF waveform is generated in accordance with a current instructionvalue or a laser output instruction value.

As a method for generating the reference transistor ON/OFF waveform, anexplanation will now be given for an example wherein the ON/OFF state ofthe transistor is defined in accordance with a specific current value inthe hysteresis comparator control process shown in FIG. 9.

At this time, the inclination when the current is increased is aconstant α1, which is determined using the value (R1/L1), and theinclination when the current is reduced is a constant α2, which is alsodetermined using the value (R1/L1).

When the current value whereat the transistor is turned on is denoted byIon and the current value whereat the transistor is turned off isdenoted by Ioff, the time Ton, during which the transistor is ON, andthe time Toff, during which the transistor is OFF, are represented byTon=(Ion−Ioff)/α1  Equation 11Toff=(Ioff−Ion)/α2  Equation 12

These represent relationships existing after the constant current valuehas been obtained, and the transistor has been remained in the ON stateuntil the constant current value has been reached.

When the current instruction value is denoted by I1, the ON time Ton1 isrepresented byTon1=I 1/α1  Equation 13

The time Toff1, from the constant current value to the current 0 A, isrepresented byToff1=I 1/α2  Equation 14

The ON/OFF time for the transistor provided using these equations can beemployed as the reference waveform.

Of course, the ON/OFF waveform of the transistor may actually bemeasured for use as the reference waveform.

Based on the reference waveform, as shown in FIG. 10 the interval (B inFIG. 10) from the ON time state for the reference waveform to the OFFtime state for the monitor value is measured to determine whether theinterval falls within the permissible range (Din FIG. 10) for the OFFtime for the reference waveform.

Either this, or the interval (C in FIG. 10) between the ON time and theOFF time for the monitor value is measured and is compared with theinterval (A in FIG. 15) between the ON time and the OFF time for thereference waveform to determine whether the interval falls within thepermissible range.

The interval between the ON and OFF time states in one cycle has beenemployed for the determination. However, the interval between the ONtime states or the interval for one cycle or more may be employed forthe determination.

Based on the above determination results, an error signal is output tothe oscillator controller 26.

With this configuration, since it can be confirmed that in accordancewith the ON/OFF signal the transistor is operated normally, it can bedetermined upon the occurrence of a current waveform abnormality whetherthe control signal (e.g., the ON/OFF signal for the transistor) isabnormal, or whether, even though the control signal is normal, thecharacteristic of the reactor or the laser diode that determines thecurrent waveform is abnormal.

That is, upon the occurrence of a laser output abnormality, it can bedetermined that the abnormality has occurred either at the lightamplification portion or the power supply portion, and in addition, fora power supply abnormality, the location of the failure can be preciselyidentified.

As is described in detail, according to the present invention, since ashifting of the monitor value from the reference waveform can bedetected, upon the occurrence of a laser output abnormality it can besurely determined that an abnormality has occurred either at the lightamplification portion or at the power supply portion. As a result, thelocation of the failure can be easily identified.

INDUSTRIAL APPLICABILITY

As is described above, according to the invention, since a failure ofthe laser oscillator can be detected, the location of a failure can beeasily identified. Thus, the laser oscillator according to the inventionis appropriate means for improving the operational efficiency.

1. A laser oscillator that, in accordance with a laser output instruction value or a current instruction value that is input, excites a laser medium and obtains a desired laser output comprising: reference waveform generation unit for employing said laser output instruction value or said current instruction value to generate a laser output waveform and a current waveform, which are references; a first comparison unit for obtaining a current monitor value, used to excite said laser medium, and for comparing said current monitor value with said current waveform generated by said reference waveform generation unit; and a second comparison unit for fetching a laser output monitor value, output by exciting said laser medium, and for comparing said value for said laser with said laser output waveform generated by said reference waveform generation unit, wherein an abnormality is detected.
 2. The laser oscillator according to claim 1, further comprising: a third comparison unit for fetching an ON/OFF signal for a main circuit device for controlling a current that flows across a laser diode that excites said laser medium or a monitor signal for said main circuit device, and for comparing said ON/OFF signal with an ON/OFF signal for said main circuit device that is generated by said reference waveform generation unit based on said laser output instruction value or said current instruction value.
 3. The laser oscillator according to claim 1, wherein a predetermined permissible range is set for a reference waveform for the comparison performed by said comparison unit.
 4. The laser oscillator according to claim 1, wherein the current waveform is generated using the following equations: I=α×twhen 0 ≦t≦(I 1/α) I=I 1 when (I 1/α)≦t where α is a constant value, I1 is the current instruction value, and t is time required for the current value to attain a desired value.
 5. The laser oscillator according to claim 1, wherein said laser output waveform is generated using the following equations: P=β×(α×t−γ) when 0≦t≦(I 1/α) P=β×(I 1−γ) when (I 1/α)≦t where α is a constant value, β denotes a proportional constant, γ denotes a threshold current, and I1 is the laser output instruction value.
 6. The laser oscillator according to claim 1, wherein at least one of said laser current waveform and said laser output waveform is generated based on a stepped approximation of an actual current waveform.
 7. The laser oscillator according to claim 1, further comprising a current controller receiving at least one of the laser output instruction value and the current instruction value and driving a laser diode and wherein said at least one of the laser output instruction value and the current instruction value are input into the reference waveform generation unit.
 8. The laser oscillator according to claim 7, wherein when the abnormality is detected by at least one of the first and the second comparison unit, an error signal is output by the at least one of the first and the second comparison units to an oscillator controller.
 9. The laser oscillator according to claim 2, wherein the third comparison unit fetches the ON/OFF signal output by a transistor that turns ON/OFF current supplied to the laser diode.
 10. The laser oscillator according to claim 3, wherein the permissible range is determined based on a variance in inclination of a current due to a variance in characteristics of the reactor and a laser diode, parallel shifting of the current value due to offset shifting of a current sensor, and variances in maximum current value and minimum current value produced by turning on and off a transistor.
 11. A method for detecting whether an abnormality has occurred in a laser beam amplification portion or a power source portion of a laser oscillator, the method comprising: inputting at least one of a current instruction value and a laser output instruction value; transmitting the at least one of the current instruction value and the laser output instruction value to a power supply unit that supplies current to a laser diode of the laser oscillator; transmitting the at least one of the current instruction value and the laser output instruction value to an abnormality detection unit; generating by the abnormality detection unit a reference waveform using one of the current instruction value and the laser output instruction value; receiving at least one of a current monitoring value from a sensor monitoring current from the laser diode and a laser output monitoring value detected from a laser medium excited by the laser diode; comparing each of the received at least one of the current monitoring value and the laser output monitoring value with a respective generated reference waveform; and outputting an error message indicating that the abnormality has occurred in the laser beam amplification portion or the power source portion of the laser oscillator based on the comparison.
 12. The method according to claim 11, further comprising setting a permissible range for each of the generated reference waveform and wherein said comparison comprises determining whether each of the received at least one of the current monitoring value and the laser output monitoring value has been shifted out the set permissible range of the respective generated reference waveform, and wherein, when said comparison determines that a received value of the received at least one of the current monitoring value and the laser output monitoring value has been shifted out the set permissible range of the respective generated reference waveform, said outputting operation is performed. 